Ten Years of Operational Experience on HRC for Remote CSO System

The city of Bremerton, Washington had been considering the use of a high rate clarification (HRC) process to treat wet weather induced flows to reduce combined sewer overflows (CSO). In December of 1999, HRC pilot testing was conducted at the Bremerton West Side Wastewater Treatment Plant (West Side) with a trailer-mounted pilot unit to test its effectiveness. The HRC pilot testing demonstrated that a high quality effluent could be produced even during variable influent loading conditions at constant overflow rates of 2,310 liters per day per square meter, lpm/m2 (55 gallons per minute per square foot, gpm/ft2). In 2001, construction was started on a 75.7 million liters a day, MLD (20 million-gallon a day, MGD) Actiflo® facility to treat wet weather induced flows, with the East Side Treatment Plant (East Side) scheduled to become operational in late 2001. The HRC approach saved Bremerton in excess of 30 million compared to traditional treatment plant expansion and conveyance and allowed for a fast tracked construction schedule to meet a consent decree imposed deadline.East Side was the first and is one of only a few satellite treatment facilities in the United States that is designed solely to treat CSOs using the HRC process. This paper reports on the operational history of the HRC limited use CSO treatment facility and the unique challenges this entails.